Comparative size evolution of marine clades from the Late Permian through Middle Triassic

Abstract.-The small size of Early Triassic marine organisms has important implications for the ecological and environmental pressures operating during and after the end-Permian mass extinction. However, this "Lilliput Effect" has only been documented quantitatively in a few invertebrate clades. Moreover, the discovery of Early Triassic gastropod specimens larger than any previously known has called the extent and duration of the Early Triassic size reduction into question. Here, we document and compare Permian-Triassic body size trends globally in eight marine clades (gastropods, bivalves, calcitic and phosphatic brachiopods, ammonoids, ostracods, conodonts, and foraminiferans). Our database contains maximum size measurements for 11,224 specimens and 2,743 species spanning the Late Permian through the Middle to Late Triassic. The Permian/Triassic boundary (PTB) shows more size reduction among species than any other interval. For most higher taxa, maximum and median size among species decreased dramatically from the latest Permian (Changhsingian) to the earliest Triassic (Induan), and then increased during Olenekian (late Early Triassic) and Anisian (early Middle Triassic) time. During the Induan, the only higher taxon much larger than its long-term mean size was the ammonoids; they increased significantly in median size across the PTB, a response perhaps related to their comparatively rapid diversity recovery after the end-Permian extinction. The loss of large species in multiple clades across the PTB resulted from both selective extinction of larger species and evolution of surviving lineages toward smaller sizes. The within-lineage component of size decrease suggests that only part of the size decrease can be related to the end-Permian kill mechanism; in addition, Early Triassic environmental conditions or ecological pressures must have continued to favor small body size as well. After the end-Permian extinction, size decrease occurred across ecologically and physiologically disparate clades, but this size reduction was limited to the first part of the Early Triassic (Induan). Nektonic habitat or physiological buffering capacity may explain the contrast of Early Triassic size increase and diversification in ammonoids versus size reduction and slow recovery in benthic clades

Rego_genus_summary2

Genus-level summary of size data, including mean, maximum, and minimum sizes across species within a genus (using the species-level maximum size for the appropriate stage for each calculation). Stratigraphic ranges within the dataset are also provided for each genus

Within- and among-genus components of size evolution during mass extinction, recovery, and background intervals: a case study of Late Permian through Late Triassic foraminifera

One of the best-recognized patterns in the evolution of organismal size is the tendency for mean and maximum size within a clade to decrease following a major extinction event and to increase during the subsequent recovery interval. Because larger organisms are typically thought to be at higher extinction risk than their smaller relatives, it has commonly been assumed that size reduction mostly reflects the selective extinction of larger species. However, to our knowledge the relative importance of within- and among-lineage processes in driving overall trends in body size has never been compared quantitatively. In this study, we use a global, specimen-level database of foraminifera to study size evolution from the Late Permian through Late Triassic. We explicitly decompose size evolution into within- and among-genus components. We find that size reduction following the end-Permian mass extinction was driven more by size reduction within surviving species and genera than by the selective extinction of larger taxa. Similarly, we find that increase in mean size across taxa during Early Triassic biotic recovery was a product primarily of size increase within survivors and the extinction of unusually small taxa, rather than the origination of new, larger taxa. During background intervals we find no strong or consistent tendency for extinction, origination, or within-lineage change to move the overall size distribution toward larger or smaller sizes. Thus, size stasis during background intervals appears to result from small and inconsistent effects of within- and among-lineage processes rather than from large but offsetting effects of within- and among-taxon components. These observations are compatible with existing data for other taxa and extinction events, implying that mass extinctions do not influence size evolution by simply selecting against larger organisms. Instead, they appear to create conditions favorable to smaller organisms

Data from: Within- and among-genus components of size evolution during mass extinction, recovery, and background intervals: a case study of Late Permian through Late Triassic foraminifera

One of the best-recognized patterns in the evolution of organismal size is the tendency for mean and maximum size within a clade to decrease following a major extinction event and to increase during the subsequent recovery interval. Because larger organisms are typically thought to be at higher extinction risk than their smaller relatives, it has commonly been assumed that size reduction mostly reflects the selective extinction of larger species. However, to our knowledge the relative importance of within- and among-lineage processes in driving overall trends in body size has never been compared quantitatively. In this study, we use a global, specimen-level database of foraminifera to study size evolution from the Late Permian through Late Triassic. We explicitly decompose size evolution into within- and among-genus components. We find that size reduction following the end- Permian mass extinction was driven more by size reduction within surviving species and genera than by the selective extinction of larger taxa. Similarly, we find that increase in mean size across taxa during Early Triassic biotic recovery was a product primarily of size increase within survivors and the extinction of unusually small taxa, rather than the origination of new, larger taxa. During background intervals we find no strong or consistent tendency for extinction, origination, or within- lineage change to move the overall size distribution toward larger or smaller sizes. Thus, size stasis during background intervals appears to result from small and inconsistent effects of within- and among-lineage processes rather than from large but offsetting effects of within- and among-taxon components. These observations are compatible with existing data for other taxa and extinction events, implying that mass extinctions do not influence size evolution by simply selecting against larger organisms. Instead, they appear to create conditions favorable to smaller organisms

Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: implications for tempo and mode of biotic recovery from the end-Permian mass extinction: Paleobiology, v

Abstract.-Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems

Rego_species_summary2

Sizes of the largest specimens for each species in each stage, compiled from the specimen-level data. Also included are the observed stratigraphic ranges for each species

Data from: Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: Implications for tempo and mode of biotic recovery from the end-Permian mass extinction

No description availabl

Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: implications for tempo and mode of biotic recovery from the end-Permian mass extinction

Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems

Rego_specimens2

Specimen-level data used as the basis for all analyses. Data were obtained by measuring figures in published monographs or compiling them from published tables

payne_occurrence_size

tab delimited text file containing list of occurrences and specimen sizes for each sampl